Lycoming 360 high oil pressure

About 350 smoh trouble free hours on my Lycoming 360-b1e in my -7. The last few flights, I've noticed my oil pressure running in the low 90s ( a little past green range ) with oil temps at 170ish.

Oil pressure used to run lower, near 75 or so.

I replaced the vdo style pressure sending unit, which had failed internally. It was leaking oil inside
which was reading generally accurately, but high by 5-10 psi.

I've verified the pressure reading with another gauge.

My relief valve has the same 6 shim washers in it since the overhaul was performed.

As an experiment on the ground, I removed the washers from the relief valve. This caused lower rpm oil pressure to decrease to 40, but will still go right to 90psi at operating rpm. This test was done without the engine fully warmed up though, with oil temps near 140

I understand Lycoming allows 115psi during warm up

Any input on the next direction to go? Or should I take a washer or two out and forget about it?

Caleb

Check breather tube

Just today had a discussion about oil pressure with an A&P and he mentioned a situation where a small or otherwise restricted breather hose cause high enough pressure to cause issues with crankshaft seal.

Norcalrv7 said:

As an experiment on the ground, I removed the washers from the relief valve. This caused lower rpm oil pressure to decrease to 40, but will still go right to 90psi at operating rpm. This test was done without the engine fully warmed up though, with oil temps near 140

Caleb

Click to expand...

This would seem to imply that the relief can shed an adequate amount of flow at lower volumes, but not at higher volumes. Pump volume increases with RPM and the ball must come progressively further off the seat and shed more oil as this volume increases in order to hold a steady pressure. Pulling 6 washers out and not seeing a single PSI drop at cruise RPM, would seem to indicate an issue with the relief circuit. Possibly the cage is damaged, keeping the ball from coming off the seat enough or their is blockage in the drain circuit from the relief valve. I don't see how reducing spring pressure would not reduce system pressure, at least some, if everything is working properly in the relief circuit. If this were not a new problem, I would suggest that the wrong spring was installed.

Larry

lr172 said:

This would seem to imply that the relief can shed an adequate amount of flow at lower volumes, but not at higher volumes. Pump volume increases with RPM and the ball must come progressively further off the seat and shed more oil as this volume increases in order to hold a steady pressure. Pulling 6 washers out and not seeing a single PSI drop at cruise RPM, would seem to indicate an issue with the relief circuit. Possibly the cage is damaged, keeping the ball from coming off the seat enough or their is blockage in the drain circuit from the relief valve. I don't see how reducing spring pressure would not reduce system pressure, at least some, if everything is working properly in the relief circuit. If this were not a new problem, I would suggest that the wrong spring was installed.

Larry

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This is a problem that has started (or at least wasn't indicated with the old sending unit) very close to a recent oil change. I see that there is another pressure relief valve that is not adjustable located in the filter adapter, could this be related?

Caleb

I would be very happy with the oil pressure numbers you're seeing.

Norcalrv7 said:

This is a problem that has started (or at least wasn't indicated with the old sending unit) very close to a recent oil change. I see that there is another pressure relief valve that is not adjustable located in the filter adapter, could this be related?

Caleb

Click to expand...

No. That is not a pressure relief, just a bypass in case the filter gets clogged. It won't affect the pressure downstream from the filter. As Bob mentioned, 90 PSI is not, in it's self, a bad thing. However, the lack of change from removing washers would seem to indicate an issue that needs to be resolved, lest it get worse.

Larry

Norcalrv7 said:

This is a problem that has started (or at least wasn't indicated with the old sending unit) very close to a recent oil change.

Caleb

Click to expand...

It is possible that a thicker oil is causing the higher pressure, if the issue truly arose at an oil change. I suspect that will be tough to determine, given the issues with your previous sensor. Hard to know if the oil change just coincided with a further degradation of the sensor. However, an oil change could rule it out.

Larry

An indication problem

After much troubleshooting, I am convinced my issue was a indication ( or lack of). With the new vdo sending unit, cruise oil pressure runs consistently around 70 psi once warmed up to 180 degrees. I only see pressures in the high 90's before the oil is warmed up (all within limits). I have decided that this has probably always been the case, but the old sending unit wasn't ever indicating it.

Thanks for the input!

Caleb